Use # in front of the keywords you focus.This will add more value to your keywords you are targetting.
Twitter provide the search results based on this hash tag only. If you use hash tag in front of a keyword and when some one searching for that word in twitter your post will be there in the results.
It's kind of like adding a tag to a blog post. If you click the hashtag, it shows all other recent posts using that same hashtag.
And it's a great way to track your campaings. If you are running contests for example.. You can also use it to your advantage by posting links to your articles with the most popular hashtashs included. In this way you can get traffic (there is a hundrends if not thousands of poeple who are clicking on those Trending: Worldwide hashtags. Use it wisely.
When u add # in b4 any keyword (without space) in any tweet, then u have created an harsh tag. People use it 4 organising info on twitter. 4 E.g.Let's say u sometimes talk about skating on twitter. U can create d harshtag #skating 2 keep track of all ur skating related tweets nd know peoples response 2 it too.